While thieves were busy looting diamonds worth Rs 250 crore from inside the high security zone of the Brussels airport on February 19, it was business as usual in the world's biggest diamond cutting centre - Surat.

It is believed that at least 90 per cent of the stolen sparklers were meant for polishing units in Surat. These units, known for putting the shine on nine out of 10 diamonds in the world, enjoy an annual turnover pegged at Rs 80,000 crore.

Yet, Surat has never seen a Brussels-type heist. The secret perhaps lies in its unbelievably simple trade system founded entirely on trust. It is a system that could give corporate lawyers and executives a nightmare because of its informal nature, but it works perfectly well for Surat's businessmen. The Brussels incident has rattled some of Surat's top diamond merchants into rethinking its loose security system . But it is unlikely that this will lead to any alterations in how crores change hands in this city. Here is why.

Every day at 4pm, Naresh Thumar leaves from his small polishing unit in Katargam on a motorcycle for the Mahidharpura diamond market. Clad in jeans, a loose shirt and sandals , Thumar carries polished diamonds that are often worth more than Rs 3 crore. He has no bodyguards with him and no locked briefcase cuffed to his wrist. He carries the sparklers, wrapped in butter paper , tucked into a tailored banian stitched with hidden pouches.

Thumar heads straight for the diamond dealers, and squatting on a plank, on shop steps or his motorcycle displays the sparklers on a blue felt-lined tray. If Thumar and the dealer settle on a price, he is handed a chit that mentions the carat weight of his diamonds, their price and the payment period. For Thumar , this tiny chit is the sole trade document and guarantee of payment.

The two diamond markets at Varachha and Mahidharpura in Surat are abuzz with tens of hundreds of diamond manufacturers and merchants. From 10 am to 6:30 pm, polished and rough diamonds worth over Rs 400 crore are traded every day. Effectively then, each man walking these streets is a crorepati. Except for the CCTV cameras installed inside the offices of some diamond merchants , there are no traces of organized security in these localities.

Around 50 per cent of the diamonds that reach the markets at Varachha and Mahidharpura land up in safe deposit vaults. There are a total of 15 vaults in both the markets where Rs 700 crore worth of diamonds are stored. If a dealer cheats, he is simply kicked out of the circle forever and his debt is shifted to other family members.

Surat has more than 3,500 large and small diamond manufacturing units employing around 4.5 lakh workers. Like most of the complexes housing diamond manufacturing units, the Diamond World Towers and the Princess Towers in Varachha's Mini Bazaar have 'light security' , a euphemism given that you can only see a few baton-wielding guards who spend most of their time asking people to park their vehicles properly.

The last stage of the diamond trade is left to an informal courier service known as angadias. They take consignments of polished stones from the big diamond companies and merchants to Mumbai. They often use trains and buses and carry the diamonds in stitched pockets of their inners or in their baggage. The diamonds are finally delivered to traders at Mumbai's Opera House for export.

The informal courier service in the diamond capital of the country is run entirely by 15 to 20 angadia firms, each of which transport diamonds worth Rs 50-60 crore every day. These men wear no uniform and their strength is their ability to blend with the crowds.

The Surat system rests on a tightknit , secretive network of families of thousands of manufacturers, dealers and importers. Almost all those in the diamond industry come from small towns like Palanpur or from Saurashtra . New recruits have to be vouched for by working angadias before they are taken on by units.

"Even without any security or surveillance cameras, it is difficult for thieves to get away with the diamonds. The market is always abuzz with tens of hundreds of traders and manufacturers and they get caught easily," says Dinesh Navadia, president, Surat Diamond Association ( SDA). But Navadia adds that after the Brussels robbery, the industry is planning to approach the state government for a special protection force.

"In my 25 years of service in the industry, I have only heard of a few small incidents. But in the recent Brussels heist, two Surat-based DTC sightholder companies lost more than Rs 200 crore worth of diamonds," says K K Sharma, former executive director, Indian Diamond Institute (IDI). Naresh Gabani, a diamond dealer in Mahidharpura diamond market, claims that the diamond markets in Surat and Mumbai are safer than the diamond district of Antwerp and the high street jewellery stores in UK and US. "We have a knack of identifying outsiders entering the markets or even at the diamond manufacturing facilities," he says.